First, we have to understand something about political demography. It’s this: We are increasingly unlikely to live among those who think differently than we do, especially when it comes to decisions about who should be president. We’ve been doing a hell of a lot of work here in Austin looking at presidential elections at the community levels since 1946. What we’ve found is that since the mid-1970s, communities have become increasingly politically homogenous.

Nothing evil about this. Our society has created great wealth and that wealth has given us many choices. One choice some of us have made is to live among those who are like-minded. This urge to do so is ancient.

It’s also tribal – as are our politics. We’ve not only moved to be among likeminded neighbors, but the parties have moved to represent social types more than ideas or issues. There was always a Bible Belt, for example. But only in the last 30 years has this social fact come to have political meaning. In that sense, political parties are more like tribes than groups for reasoned discussion or consistent advocacy. (See a great new book on the subject, Partisan Hearts and Minds.)

So we have increasingly isolated social groups and we have political parties that increasingly align with them. Bad combination. Political writer Stuart Rothenberg told us:

"When you start chopping up an electorate narrowly and narrowcasting messages to them, you create smaller societies that see themselves as separate. It destroys the sense of community and common interests and values. It makes it a lot easier to see your opponent in caricature terms, as not entirely patriotic or caring about old people. Each party uses these ridiculous stereotypes. . . . That does fit with an electorate and a country that is increasingly fractured."

Now, if we lived in politically competitive communities, turnout would be higher. (David Campbell at Notre Dame has found this to be true.) But we don’t. So we use an even more powerful political device to get out the vote: hate.

With fewer undecided votes and an isolated electorate, turnout is key. And the way to turn out voters is by pissing them off. Social scientists have persistently found that turnout among those who feel partisanly Republican or Democratic is higher than for those who consider themselves independents. And Ohio State University political psychologist Jon Krosnick has said that turnout is highest when voters "like one candidate and hate another."

So there we are. Or, here we are. People are grouping into likeminded groups. (The most politically homogenous institution – Democrat AND Republican – is the local church.) These likeminded groups are talking themselves into more extreme positions.

The parties are responding to this social fact of political life. And they are using the most powerful tools they can find to increase turnout in an election where turnout will determine the winner.